Internet protocol-enabled telecommunication providers in the United States are required by the Federal Communications Commission (FCC) to support enhanced 911 (E911) emergency call services. That is, when a telephone user dials 9-1-1, the telecommunication carrier must be able to process the call to determine the geographic location from where the call originated to enable dispatching of emergency personnel to the location of the 911 caller. Enhanced 911 service differs from traditional (e.g., non-enhanced) 911 service in that E911 service routes an emergency call to a 911 dispatcher and provides the dispatcher with the geographic location (e.g., street address) from which the call was originated. While traditional 911 services route an emergency call to a 911 dispatcher, it does so without providing the dispatcher with geographic location information indicating where the call originated.
In traditional public switched telephone networks (PSTN), the geographic information retrieval support for E911 is implemented via fixed associations of wire line telephone numbers to geographic street addresses. Telecommunication providers usually store a subscriber's location (e.g., a street address) in a database associated with an assigned telephone number (e.g., a call back number (CBN)) during the service activation. When a PSTN user makes a 911 call, the telephone number of the caller making the 911 call (i.e., the CBN) can be used to look up the geographic location of the caller, and the retrieved location information can be used to dispatch emergency personnel to the caller.
The introduction of voice over IP (VoIP) technology introduces various challenges to service providers seeking to support E911 services. In particular, under a nomadic service (e.g., a service that allows a subscriber to connect a VoIP telephone at various network locations), a VoIP subscriber can easily disconnect a VoIP telephone from one location (e.g., the subscriber's home and/or workplace), connect the VoIP telephone in another location (e.g., a visited local area network (LAN), a coffee shop, a vacation spot, etc.), and register the VoIP telephone with the VoIP service provider to enable the subscriber to place telephone calls from the other location. This nomadic capability of VoIP phones introduces the potential for inaccurate associations between telephone numbers and physical and/or geographic locations.